The present invention relates to a composition for coating and, more particularly, to a composition for coating capable of forming a film having excellent abrasion resistance, adhesion, heat resistance and UV-ray resistance.
In recent years, transparent plastics, which are difficult to break and light in weight are finding many uses in place of glass panels. For example, at the present time, transparent glass produced from synthetic organic polymers has frequently been employed in transportation means such as railroad cars, buses, etc., optical instruments and construction materials.
However, transparent plastics, while having the above advantages, are liable to suffer from scratches or damage to the surface, whereby its transparency may be lowered to damage its appearance. Also, transparent plastics have the disadvantage of being easily discolored when exposed to UV-rays such as sunlight for a long time.
Accordingly, various attempts have been made to improve the abrasion resistance of transparent plastics. For example, Japanese Provisional Patent Publications No. 2736/1976, No. 87736/1979 and No. 94971/1980 disclose compositions for coating, comprising an aqueous dispersion of colloidal silica and a hydrolyzable organosilane compound dissolved or dispersed in a hydrolyzing solvent such as an alcohol or water. Generally speaking, it has been attempted to prevent the plastics from UV-ray deterioration due to exposure to sunlight by coating the plastics with such a composition for coating in which a UV-absorber is incorporated.
However, most UV-absorbers have the problem of being removed from the composition during the heat curing step through, for example, volatilization. Further, they also have the disadvantage of worsening adhesion to the plastics.
For overcoming these disadvantages, a UV-absorber comprising an alkylcarbamyl adduct of alkoxysilyl or alkanoylsilyl is exemplified in Japanese Provisional Patent Publication No. 21476/1982, but this method is not only complicated in its steps, but also very disadvantageous in its economical aspects. Further, in Japanese Provisional Patent Publications No. 10591/1983 and No. 8776/1983, a UV-absorber is obtained by reacting the hydroxyl group of an aromatic UV-absorber such as 2,4-dihydroxybenzophenone, etc. with the epoxy group of an epoxy-containing silane compound in the presence of tetramethylammonium chloride, but the film obtained by heat curing with addition of this product has the disadvantage of inferior heat resistance and water resistance.